A communication system operates to communicate data between two or more locations at which communication stations, operable in the communication system, are positioned. Data, sourced at a sending station, is communicated upon a communication channel to be terminated at a receiving station. Many varied types of communication systems have been developed and communication of data through the use of such communication systems is a pervasive aspect of modern society. And the need to communicate data shall likely become increasingly pervasive in the future.
Advancements in communication technologies are implemented into existing communication systems to improve their performance. And advancements in communication technologies have permitted the implementation of new types of communication systems that provide for new types of communication services, previously unavailable.
A radio communication system is an exemplary communication system and is exemplary of a type of communication system in which advancements in communication technologies have been implemented. New types of communication services, and effectuation of conventional communication services in improved manners, are possible as a result of implementation of such advancements in communication technologies.
Communication channels defined in a radio communication system are defined upon radio links that extend between communication stations of the radio communication system. The need to utilize a conventional, wireline connection along the entire communication path extending between sending and receiving stations of the communication system is obviated. For at least a portion of the communication path, a radio link is substituted for the wireline connection. And, when the radio link is substituted for the wireline connection, the need otherwise to utilize a wireline connection along that portion of the communication path is obviated.
A radio communication system provides various advantages. Initial installation and deployment of a radio communication system is generally performed in a less costly manner than the corresponding costs required of installing and deploying a wireline counterpart. Also, a radio communication system is permitting of implementation as a mobile communication system. In a mobile communication system, one or more of the communication stations operable therein is mobile, i.e., is permitted movement.
A cellular communication system is a type of mobile communication system. Cellular communication systems have achieved high levels of usage and the network infrastructures of cellular communication systems have been installed to encompass significant portions of the populated areas of the world. Voice, and other data, services are effectuated through the use of a cellular communication system.
A cellular communication system is generally constructed to be in conformity with a standard, operational protocol promulgated by a standards-creating body, such as the EIA/TIA. Successive generations of communication standards have been promulgated, and communication systems have been implemented to be in operational conformity therewith. First-generation, second-generation, third-generation, and successor-generation operational specifications have been promulgated or are under discussion.
Several of the operational specifications set forth CDMA (Code Division Multiple Access) communication schemes, utilizing spread-spectrum communication techniques. The IS-95, IS-98, and IS-2000 operational specifications set forth the operational parameters of communication systems that utilize CDMA communication schemes. Other operational specifications set forth the operating parameters of communication systems that utilize other communication schemes, such as TDMA (time-division, multiple-access) schemes or conventional analog communication schemes.
Communication stations operable in a cellular communication system pursuant to a communication session must be in synchronization with one another so that the data that is communicated therebetween is successfully received. A delay lock loop circuit, forming part of a receiver, is sometimes used by which to place, and maintain, the receiver in synchronization with the transmitter. Such circuits are used in spread-spectrum systems as well as other cellular, and other radio, communication systems. Delay lock loop circuits, for instance, are used in communication systems operable pursuant to an IEEE 802.11 protocol, the aforementioned IS-95/IS-2000 protocols, and a WCDMA protocol. In an IS-95/IS-2000 system, the receiver utilizes a pilot signal broadcast during operation of such a communication system, to place the receiver in synchronization with a transmitter.
A delay lock loop circuit generally has two operating modes. A first mode, referred to as an acquisition mode, is first used during initial synchronization when the initial timing between the transmitter and receiver is only coarsely known. In this mode, the delay lock loop circuit attempts to align the receiver and transmitter in a quick manner. Thereafter, a second mode, referred to as a tracking mode, is used. In the tracking mode, the timing of the receiver is close to the correct timing epoch. And, when in the tracking mode, the delay lock loop further reduces timing errors between the receiver and transmitter.
When in the acquisition mode, the timing error is maintained with some known variance, which is dependent upon loop parameters. The amount of variance is traded-off against a desired pull-in time. When in the tracking mode, there no longer is a pull-in requirement, and the loop bandwidth of the delay lock loop circuit is changed in order to provide a tracking error that exhibits a smaller variance.
Conventionally, the architecture of the delay lock loop circuit used for the acquisition mode and the delay lock loop circuit used for the tracking mode use different loop filters.
Conventional delay lock loop circuits, however, are input signal-dependent. That is to say, the delay lock loop circuit is inherently dependent upon the input signal level of input signals applied thereto. And, thus, the circuit is constructed to be capable to receive a range of input signal levels, and circuit-construction compromises are made at other signal levels. Normalization of input signal values is sometimes required and, when the input signal is beyond the accepted range of input signal levels, the delay lock loop circuit might not perform acceptably.
Delay lock loop circuits and methods have been developed in an effort to improve the manner by which a receiver is placed, and maintained, in synchronization with a transmitter. One such system and method is disclosed by U.S. Pat. No. 6,834,087, entitled: Delay Lock Loop Circuit, and Associated Method, for a Radio Receiver, issued on Dec. 21, 2004, the contents of which are hereby incorporated by reference in its entirety. In this regard, the '087 patent provides a delay lock loop circuit that is selectively operable in an acquisition mode and a tracking mode. A selector selects operating parameters of elements of the delay lock loop circuit to cause operation of the circuit alternately in the acquisition mode and the tracking mode. Through appropriate selection of the operating parameters, a selected one of the operating modes is effectuated. As also provided by the '087 patent, the delay lock loop circuit is amplitude-independent, operable irrespective of the values of the input signals applied thereto.
Delay lock loop circuits such as that disclosed by the '087 patent overcome many drawbacks of the conventional delay lock loop circuits. As will be readily appreciated by those skilled in the art, however, it is generally desirable to further improve upon existing systems and methods, including the delay lock loop circuit of the '087 patent.